Device for converting mechanical energy into electrical energy

ABSTRACT

An apparatus for conversion of mechanical energy to electrical energy by means of a piezo transducer ( 1 ), on which an electrical voltage, which can be supplied to a load ( 8 ), is formed when deformation occurs. The piezo transducer ( 1 ) is formed from two or more layers ( 2 ) of piezoelectric material, which are separated from one another by electrically conductive layers ( 10, 11 ), and the successive electrically conductive layers ( 10, 11 ) are alternately connected to common electrical contacts ( 13, 14 ).

The invention relates to an apparatus for conversion of mechanicalenergy to electrical energy by means of a piezo transducer, on which anelectrical voltage, which can be supplied to a load, is formed whendeformation occurs. In an apparatus of this type which is known from WO98/36395, an electrical voltage, which is produced by charge shifts inthe piezoelectric material of the transducer, is generated by mechanicaldeformation of a piezo transducer. The known apparatus has a wire-freeswitch, which uses process energy, with radio signals, and this switchhas a piezoelectric transducer to which finger pressure can be appliedand which generates a piezo voltage. A code which corresponds to theambient temperature can be applied to the radio-frequency signal that isproduced by the switch. Furthermore, in order to generate a high piezovoltage, a mechanical operating apparatus with a beyond-dead-centerspring can be used, which moves beyond the dead point when loaded,suddenly applying the selected mechanical prestress to the transducer.

The object of the invention is to provide an apparatus of the typementioned initially which can be produced with relatively little effortfor operation of a load, in particular of a load which contains aradio-frequency transmitter.

According to the invention, this object is achieved by thecharacterizing features of patent claim 1.

The invention provides an apparatus for conversion of mechanical energy,in particular in the form of available process energy, to electricalenergy. The piezo transducer which is used for this purpose comprisestwo or more layers of piezoelectric material, which are separated fromone another by electrically conductive layers. All the layers aremechanically firmly connected. The successive electrically conductivelayers are alternately connected to common electrical contacts, whichcan if required be connected via supply lines to a load. The successivelayers of the piezoelectric material preferably have rising layerthicknesses. The piezo transducer, which comprises two or morepiezoelectric layers and the electrically conductive layers located inbetween them, can preferably be deformed by bending.

A deformation mechanism, which represents an invention in its own right,and has a mechanical energy store, in particular in the form of a springelement, may be used to deform the piezo transducer. The deformationmechanism may be designed such that the deformation movement duringstorage of the energy is greater than the deformation movement when themechanical energy is being emitted to the piezo transducer. For thispurpose, the deformation mechanism may be in the form of a levermechanism, which allows the desired reduction in the movement distanceto be achieved.

The spring element which forms the mechanical energy store may bedesigned such that the movement resulting from bending of the elementfrom the rest position to the dead point is greater than the movement onthe other side of the dead point after it has flipped over, on which themechanical energy is emitted in order to deform the piezoelectricmaterial. In this case, the forces behave in opposite senses, that is tosay the force which acts on the piezo transducer is amplified by thesame factor as the reduction in the movement distance. This effect isachieved not only in the case of a piezo transducer with the layerstructure explained above, but in the case of any piezo transducer whichcan be deformed, in particular, by bending. The invention also disclosesa deformation mechanism, in which a force acting on the piezo transducerand which is amplified by the factor of the movement distance reductionachieved by the lever effect is produced by the lever effect.

In order to achieve a compact design, the deformation mechanism and thepiezo transducer may be arranged in a common holder. A supportingsurface, on which the deformed piezo transducer rests, may be providedon the holder. This supporting surface may form an optimally preshapedsubstrate, against which the piezo transducer, which is deformed inparticular by pressure when mechanical energy is being released, ispressed.

The mechanical energy is preferably introduced into the piezo transducercentrally on a surface of the piezo transducer. The piezo transducer canbe mounted in or on the holder by clamping or adhesive bonding.

The load may likewise be arranged on or in the common holder. However,it is also possible to arrange the load remotely from the piezotransducer, and to supply the electrical voltage that is generated tothe load via supply lines of appropriate size.

The load includes a transmitter, which is preferably operated by theconverted energy, in particular a radio-frequency transmitter, by meansof which information which is stored in electronics provided in the loador formed by evaluation, for example from measurement signals or sensorsignals, is transmitted without the use of wires to a receiving station.For this purpose, the load may have a miniaturized circuit with amicroprocessor and with the already mentioned transmitter, in particulara radio-frequency transmitter. When the piezo transducer is operated ordeformed, the radio-frequency signal is transmitted. In addition to thealready mentioned measurement or sensor information, this signal mayinclude at least one identification number, a coding for safetyapplications, for example a rolling code method for electronic accessand the like. The receiving station may be arranged remotely, and maycontain the necessary devices for descrambling and evaluation of thetransmitted information. These can be used for controlling processes,for indication and for storage or the like.

The invention may be used in widely differing fields. For example, theinvention may be used for hand-operated switches which send theirinformation by radio or via a wire link. Further application examplesinclude electronic keys for cars, dwellings, commercial properties andthe like. Furthermore, the invention may be used for status signalingdevices for doors, windows and other objects. Furthermore, the inventioncan be used for switches in vehicles, such as automobiles and the like.Furthermore, the invention may be used for emergency call devices forpersonal protection, in hospitals, in public facilities such as trainstations and the like. The invention is preferably used withmechanically operated sensors, in machine and plant construction and invehicles, as well as in sports and recreational time appliances andtoys.

Since the apparatus according to the invention can be implemented in aminiaturized form, it has a wide range of application options.

The invention will be explained in more detail using an exemplaryembodiment and with reference to the figures, in which:

FIG. 1 shows a section through a piezo transducer which may be used forthe invention;

FIG. 2 shows an illustration, in the form of a section, through anexemplary embodiment with the deformation mechanism in the rest state;and

FIG. 3 shows the state of the exemplary embodiment when mechanicalenergy is being emitted from the deformation mechanism to the piezotransducer.

The illustrated exemplary embodiment contains a piezo transducer 1 and adeformation mechanism 17, which transmits stored energy to the piezotransducer in order to deform it. The piezo transducer 1 is for thispurpose inserted in a holder 12. The piezo transducer 1 is mounted, forexample, by clamping or adhesive bonding on the edge zones of the piezotransducer.

The deformation mechanism 17 is arranged above the piezo transducer 1and has a spring element 3 which, in the illustrated exemplaryembodiment, is curved upwards in its rest position. The spring element 3is mounted in the holder 2, which is in the form of a circular ring, bymeans of a mounting ring 6 and an elastic O-ring 5.

The spring element 3 forms a mechanical store which flexes when amechanical pressure 9 is exerted from above or from outside, withmechanical energy in the process being stored up to a specific deadpoint of the deformation. Beyond the dead point of the deformation, thespring element 3 flips over to a state in which it is curved downwards,as illustrated in FIG. 3. In the process, it emits the stored mechanicalenergy to the piezo transducer 1, which is deformed in the process.

In the illustrated exemplary embodiment, a damping element 4 is providedat the point at which energy is transmitted to the piezo transducer 1.This results in a balanced load on the piezo transducer, as well ascompensation for manufacturing tolerances. Furthermore, this results inthe mechanical energy being transmitted to the piezo transducer 1without causing damage.

The holder 12 is pot-shaped in the area in which it holds the piezotransducer 1 and the deformation mechanism 17, and has a supportingsurface 15 on its base. The deformed piezo transducer 2 is pressedagainst this supporting surface 15. The curvature of the supportingsurface 15 is matched to the optimum deformation of the piezo transducer1. The optimum bent shape of the piezo transducer is designed withrespect to the transducer protection and energy yield.

As is shown in FIGS. 2 and 3, the spring element 3 is supported on theholder via the O-ring 5 and the mounting ring 6 on the holder 12, at adistance from the point at which the mechanical energy is transmitted tothe piezo transducer 1. This results in a lever effect, by means ofwhich the stored mechanical energy is transmitted to the piezotransducer 1. This makes it possible for the deformation movement whichthe spring element 3 carries out after passing over the dead point whentransmitting the stored mechanical energy to the piezo transducer 1 tobe designed to be short, matching deformation of the piezo transducerthat causes no damage. The lever effect results in an increased forcebeing exerted on the piezoelectric material of the transducer 1. Thedeformation movement for bending of the spring element 3 from the restposition as illustrated in FIG. 2 to the dead point may advantageouslybe designed to be greater than the movement which takes place afterflipping over or after passing over the dead point, when energy is beingtransmitted to the piezo transducer 1. This results in adequatetransmission of the necessary mechanical energy, which is converted toelectrical energy in the piezo transducer 1, with little deformation ofthe piezo transducer 1. The force which acts on the piezo transducer 1is increased by the factor of the reduction in the movement distancewhich is achieved after the passing over the dead point position.

As can be seen from FIG. 1, a piezo transducer 1 with a layeredstructure is preferably used. The piezoelectric material, preferablycomposed of piezo ceramic, is arranged in layers 2 with a rising layerthickness. For the sake of simplicity, FIG. 1 shows three layers 2 ofpiezoelectric material. However, more layers may also be provided in thelayer structure.

Separating layers in the form of electrically conductive layers 10, 11are located between the layers 2 of piezoelectric material, inparticular piezoelectric ceramic. Successive electrically conductivelayers 10, 11 in the layer structure are alternately electricallyconnected to one another. This may be achieved by means of electricalcontacts 13, 14, in a similar way to that in which contact is made withcapacitor plates. In the illustrated exemplary embodiment, theelectrically conductive separating layers 10 are connected to oneanother via the electrical contact 13, and the electrically conductivelayers 11 are connected to one another via the electrical contact 14.The contact may be made, for example, by adhesive bonding, bonding,clamping or other contact-making methods.

In the case of the arrangement of the piezo transducer 1 installed inthe holder 12, the layer 2 of piezoelectric material which has the leastlayer thickness is located on the side of the piezo transducer 1 onwhich the force is introduced when it is deformed by the deformationmechanism 17. As already mentioned, the layers 2 located underneath thishave layer thicknesses which become ever greater in the sequence of thelayer structure.

All of the layers in the layer structure are mechanically firmlyconnected to one another. The layered structure of the piezo transducer1 results in a high energy density, and thus in a good miniaturizationcapability. A high degree of flexibility is available for the design ofthe mechanical and electrical parameters. The layered structure ensuresthat the piezo transducer has a long life and that it can be produced atlow cost.

As can be seen in particular from FIGS. 2 and 3, the piezo transducer 1with the layered structure may be used in such a way that central forceintroduction and bending in the central area are achieved, with supportin the edge zones. This can be clearly seen in particular from theillustration in FIG. 3.

The piezo transducer 1 may be in the form of a circular disk and may bearranged in a holder 12 in the form of a circular ring. However, it isalso possible to use a rectangular or square shape, in which the forceis introduced centrally in the form of a line, in order to bend thepiezo transducer 1.

In the illustrated exemplary embodiment, a miniaturized circuit isprovided on the lower face of the holder 12, as the load 8. This circuitmay have a microprocessor and a radio-frequency transmitter. Theelectrical voltage which is generated during deformation of the piezotransducer 1 is passed to the load 8 via electrical supply lines 7, onesupply line of which is illustrated. During the deformation of the piezotransducer 1, the radio-frequency transmitter transmits a message whichcontains information, which is stored in the miniaturized circuit or hasbeen obtained on activation by the voltage that is generated by thepiezo transducer 1. This information may include at least oneidentification number, coding and measurement and/or sensor informationand the like. The transmitted signals are received by a receiverstation, which is provided remotely and is not illustrated in any moredetail, and may be used to control processes, for indication and/or forstorage. The load 8 may be enclosed by an encapsulation compound 16 orby some other suitable protective sheath.

1. An apparatus for conversion of mechanical energy to electrical energyby means of a piezo transducer (1), on which an electrical voltage,which can be supplied to a load (8), is formed when deformation occurs,characterized in that the piezo transducer (1) is formed from two ormore layers (2) of piezoelectric material, which are separated from oneanother by electrically conductive layers (10, 11), and the successiveelectrically conductive layers (10, 11) are alternately connected tocommon electrical contacts (13, 14).
 2. The apparatus as claimed inclaim 1, characterized in that the successive layers (2) of thepiezoelectric material have rising layer thicknesses.
 3. The apparatusas claimed in claim 1, characterized in that the piezo transducer (1) isflexible.
 4. (Canceled)
 5. The apparatus, in particular as claimed inclaim 1, characterized in that a deformation mechanism (17), which has amechanical energy store (3, 5), is provided for deformation of the piezotransducer (1).
 6. The apparatus as claimed in claim 5, characterized inthat the deformation movement of the deformation mechanism (17) duringthe storage of mechanical energy is greater than when the mechanicalenergy is emitted to the piezo transducer (1).
 7. The apparatus asclaimed in claim 5, characterized in that the deformation mechanism (17)is in the form of a lever mechanism.
 8. The apparatus as claimed inclaim 5, characterized in that the energy store (5) has a spring element(3).
 9. The apparatus as claimed in claim 8, characterized in that thespring element (3) has a dead point, with the spring element (3) storingmechanical energy when it is deformed on one side of the dead point, andemitting mechanical energy to the piezo transducer (1) on the other sideof the dead point.
 10. The apparatus as claimed in claim 1,characterized in that the mechanical energy is introduced into the piezotransducer (1) via a damping element (4).
 11. The apparatus as claimedin claim 1, characterized in that the deformation mechanism (17) and thepiezo transducer (1) are arranged in a common holder (12).
 12. Theapparatus as claimed in claim 1, characterized in that a supportingsurface (15), on which the deformed piezo transducer (1) rests, isprovided on the holder (12).
 13. The apparatus as claimed in claim 1,characterized in that the mechanical energy is introduced centrally on asurface of the piezo transducer (1).
 14. The apparatus as claimed inclaim 1, characterized in that the layer (2) of the piezoelectricmaterial with the least layer thickness is located on that side of thepiezo transducer (1) on which the mechanical energy is introduced duringthe deformation of the piezo transducer.
 15. The apparatus as claimed inclaim 1, characterized in that the piezo transducer (1) is mounted onits edge zones in the holder (12) by means of clamping or adhesivebonding.
 16. The apparatus as claimed in claim 1, characterized in thatthe load (8) is likewise arranged on or in the common holder (12). 17.The apparatus as claimed in claim 1, characterized in that the load (8)has a transmitter which is operated by the converted energy.
 18. Theapparatus as claimed in claim 17, characterized in that informationwhich is transmitted by the transmitter has at least one identitynumber.